Electron device with long electron path



Jan. 12, 1954 A, M. cLoGsToN ELECTRON DEVICE WITH LONG ELECTRON PATH 5 Sheets-Sheet l Filed Dec. 29, 1951 Jan. 12, 1954 A. M. cLoGsToN f 2,666,163

ELECTRON DEVICE WITH LONG ELECTRON PATH Filed Dec. 29, 1951 F/G. 5A

TIME our M/c/PosEco/vos NME OUT-MICROSECONDS 5 Sheets-Sheetl 2 SIGNAL INPUT NO.

l I I a /0 20 UME /N M/CROSECONDS /NVENTOR A. M cLoGsro/v Jan. 12, i954 A M CLOGSTQN 2,666,163

ELECTRON DEVICE WITH LONG ELECTRON PATH -Filed Dec. 29, 1951 3 Sheets-Sheet 5 A. M. CLOGsro/v Patented Jan. 12, 1954 ELECTRON DEVICE WITH LONG ELECTRON PATH Albert M. Clogston, Morris Plains, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 29, 1951, Serial No. 264,018

13 Claims. (Cl. 315-21) This invention relates to apparatus for delay' ing electrical signals and more specically to cathode-ray delay devices.

It is an object of this invention to improve the versatility of devices for delaying electrical signals.

It is another object of this invention to make readily variable the electrical time delay in cathode-ray delay tubes.

It is still another object of this invention to vary the length of the physical path traveled by a beam in a cathode-ray tube.

There has long been a need in the communication and other electrical arts for a device which produces an elastic time delay for applied signals, that is, a delay which can be varied quickly and easily. Such a device would be of considerable importance in electric circuits for delaying electrical pulses by varying amounts. Moreover, such a device would be of great value in encoding systems where it is desired to change the order and/or spacing of pulses in a series and in a variety of other systems in which signal time delay is required.

Passive delay circuits have been used to a great extent in various circuit arrangements but they are not generally variable and, for relatively large delays, require considerable apparatus. Acoustic delay lines have also been suggested for Various circuit arrangements but they also have the disadvantage that the delay of the signal cannot readily be varied and the attenuation is very large.

Various electronic devices have been used in circuits requiring time delays, the electronic storage tube being the best known example of this type of device. In such a tube, a signal modulated beam is caused to scan a target to build up charges in various elemental portions thereof which can be stored for a limited period of time. These'charges are removed by a second beam or by the storing beam if appropriate switching circuits are provided. The output signal available in tubes of this character is limited l because of the relatively small cross-sectional area of the beam (made necessary by the small size of the elemental storage area). Moreover, the time delay imparted to the signal by tubes of this type cannot be simply varied nor is it an easy matter to change the order of the signal pulses in the reading (output) circuit compared to the order of signals in the writing (input) circuit.

path being in the form of a helix extending from the cathode to a collecting electrode, for example. Four elds act upon the electron beam: a magnetic circumferential field, a. magnetic longitudinal eld, an accelerating electric field, and a transverse electric field. Any one of these fields can be varied but as a practical matter it is easier to vary the two electric fields than it is to change the value of the two magnetic elds once they have been adjusted to predetermined values for the particular installation. The two magnetic elds in combination tend to restrict the path of the beam in the tube to a helix but this helical path is changed somewhat by the two electric fields. Variation of the accelerating electric i'ield varies the delay mainly by altering the speed of the electrons in the stream, while variation of the transverse electric field changes the delay time chiefly by changing the pitch of the helix.v The number of electrons in the beam can beA made very large since it is not necessary to re strict the cross-sectional area of the beam to the area of an elemental area of a. target because the target in the present invention serves only asa collector electrode and is relatively large com-- pared to an elemental area in a storage tube' target.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawingsv forming a part thereof, in which:

Fig. 1 is a schematic'longitudinal sectional view of a cathode-ray device in accordance with the invention for producing elastic time delays;

Fig. 1A is a schematic enlarged view of the@ electron source in the arrangement of Fig. 1;

Fig. 2 is a cross-sectional view of the tube in j the arrangement of Fig. l taken in a planel through the line 2 2 in the latter` figure;

Figs. 3A and 3B are diagrammatic representations to aid in understanding the invention;

Fig. 4 is a longitudinal view of a modification of the arrangement of Fig. 1;

tric field, respectively;

2 In accordance with the present invention, ther p is provided a cathode-ray tube in which the path Fig. 6 shows one collector arrangement for the invention; and

Fig. 7 shows another form of collector.

For a more detailed description of the invention, reference will now be made more specifically to the drawings. In these drawings, Fig. 1 shows a cathode-ray device ID, in accordance. with the invention, for imparting elastic time delays to signals applied thereto and which comprises a tube II and various associated circuit elements. Specifically, these circuit elements include three input circuits identified in the drawing'as Signal Input No. 1, Signal Input No. 2, and Signal Input No. 3, respectively, an output circuit identified in the drawings as Signal Output, and-circuits for applying potentials to magnetic coils I2 v.and I3 for forming circumferential and longitudinal magnetic elds, respectively. Biasing sources are included in the respective input and output circuits.

The tube iii comprises agrounded hollow cylindrical metallic envelope I4 serving as an anode and having an annular evacuated 4chamber I5 in which there are positioned .at opposite ends an electron source. or kgun i6 andan annular collector electrode I7. A beam of electrons, represented by the dash-dot line A, is caused to travel ya helical path in the tube between the members I6 kand I1 (by means. of magnetic and electric eld producing means to be described below in detail), and, by means of signals applied to the various input circuits, themode of travel of the electrons in the beam can be controlled in any of avariety of ways.

Within the chamber I is a cylindrical conductor or shell I8 which is connected to the Signal Input No. lthrough an appropriate coupling condenser I9.. A biasing transverse electric field -E between the envelope I4 and the shell I8 is obtained lby connecting the memberi t0 ground through -a resistance Z0 and a potential source 2|. This biasing voltage, which is. of the order of 10, volts for example, may be poled in either direction by the reversing switch v22 connected in circuit with the .source 2 I. A signal applied to Signal Input No. .1 varies the intensity of the eld E and'thus varies the time delay of the electrons in the beam between the members I6 and I1 by varying the pitch ofthe helical path between the gun I6 and the collector I1.

vSignal Inputs Nos. 2 and 3 control the electron gun I6, a specific 'illustrative embodiment of which is shown in Fig. 1A. The gun IB comprises a cathode 3G, a cathode heater 3i, and a control-element 32,. Current for ythe heater cathode .is obtained from a source `33 by means of transformer `34 and wires .35, and-.36, The Signal Input No. 2 is connected through the coum pling condenser V3,1-and wire38 to the control element v`32 while the cathodev 3l is connected )by means of wire 39 and coupling condenser 40 to theSignal` Input'No. 3. Bias for the control element 32 is obtained by means of sources 4I and 42 through yresistors 43 and 44. Signal yInput No. 2' controls the number of electrons in the beam and signals modulating the intensity of the beam areappliedlat this point'. SignalInput No. 3i controls the speed of the electrons and signalsiappliedthei'e vary the delay of the electronsxin the; beam Aby said control. The intensity of the accelerating, electricfield Vais determined'byvthe sum-ofthe voltage Vaoffrom source Hand .the- .voltage applied to Signal Input No.. 3.. Tha intensity .of rthe transverse electric field E is determined by the sum of the voltage Vsmffrom 'tentiaL 4 source 2l and the voltage applied to Signal Input No. 1.

The signal output circuit is connected to the control electrod I1. The collector is placed at an appropriate positive potential with respect to the electron gun IB by means of the source of potential 46. This source may be, for example, of the order of five or six volts above ground and ten or twelve volts with respect to cathode po- There is nothing critical about the voltage between the cathode and the collector except that it should not be high enough to produce more secondary electrons from the collector I'I than there are primary electrons in the beam striking it.

'Io provide a longitudinal magnetic field Bz, the coil I3 is Wound in the form of a solenoid around the envelope I4. A voltage V2 is applied to the Icoil I3 vbv ymeans of a suitable source 5I which may be varied to give the desired iield intensity BZ. A circumferential Vmagnetic iield B is obtained by `means of toroidal voltage coil I2 wrapped as shown in Figs. 1 and 2. A voltage V1 -is applied to `th-is coil bymeans of source 52 to produce the desired intensity of circumferential eld B. The source 52 may be varied to produce any desired eld strength.

The operation of thedevice shown in Figs. l and 2 will now be described. The sources 5I and 5,2 are adjustedso that they tend to direct the beam from the cathode .30 ina helical path to the collector I'I. This helical rpath is varied somewhat (but it is still helical) by the accelerating electric field Va and the transverse electric field E. A signal applied to Signal Input No. 1, `which varies Vtheintensity of vthe transverse electric iield E, will vary the pitch of the helix of the beam and hence varies the delay time. Variation of the Vgrid voltage Vg, either by changing the voltage Vg., of the source 42 or by applying a signal to the Signal Input No. 2, will vary the numberof electrons in the beam A. Variation of the cathode voltage, either by varying the potential Va, of the source 4I or by applying signals to the Signal Input No. 3 will vary the potential of the accelerating electric eld Va and hence the speed of the electrons. Summarizing', then, there are four eld values which can 'be varied, that is, the accelerating electric eld Va, the transverse delectric eld E, the longitudinal magnetic eld Bz, and the circumferential magnetic field B. Since in practice, it is more difficult to vary the magnetic elds than it is to vary the electric fields, control signals are applied, as shown inthe drawings, to the elements lwhich varytheelectric fields only, but it is to be understood that the magnetic elds can be varied by control signals as well.

The frmula for the .delay in seconds can be written:

"ZeVa V, *W14- I (l) tudinal magnetic field (Webers/meterz).

If someA of the constants in the above equation are given the following values by way of example:

B=0.01'Webers/meter2 R=0.028 meter and W=0.001 meter the equation becomes croseconds and accelerating voltage Va for different values ofivoltage Vs, the set ofY curves in Fig. 3A being taken for magnetic vleld strengths of B of 100 gauss and BZY of -5 gauss While the lower curves are taken for negative values of Vs and B is '-100 gauss, Bz remaining at -5 gauss.

The device shown in Figs. 1 and 2 has many advantages. Due to the size and'sh'ape of the collectorA electrode, there is no electro-optical problem of making a beam ofaccurate size and, moreover, the output 'signal available is not limited to a narrow beam (as in many other electronic storage tubes) and, as a matter of fact, the beam can have a relatively large intensity. The information "Write in is continuous and no erasing is required, nor is it necessary to switch between Ytwo tubes, one of which is writing the information to be stored and the Aother of which is reading the stored information. The time delay is measured by the length of time the beam takes to cover the path between the cathode and the collector but this can be made relatively large such as of the order of 100 microseconds, for example. To obtain such delays the path length is made very long, that is, tens or hundreds of feet although it is obvious that the tube itself is by no means this long. Y

In addition to its value for delaying signals by a time period which can be quickly and readily changed by varying the potential of the accelerating voltage or of the transverse voltage, the device of this invention is very useful in encoding systems. For example itcan be used to open up time gaps at the transmitting and receiving ends of a system by varying the velocity of some electrons more than others.

In order to understand this last statement, it should be noted that a change of Va or E affect a chain of pulses going through the delay tube in different ways. When E is varied by a changing signal in Signal Input No. 1, all pulses in the drift space between the gun I6 and the collector I1 are affected, while a change in V (by changing the voltage in SignalInput No. 3) affects only those pulses that enter the drift space after the change. This difference is illustrated in Figs. 5A and 5B where the time period between the start of the pulse chain and the time when a particular pulse in the chain `reaches the collector (time out) is plotted against the time period between the start of the pulse chain and the time the particular pulse modulates the stream (time in), Fig. 5A represents an illustrative condition when signals are applied to Signal Input No. 1 (changing E) and Fig. 5B shows the condition when similar signals are applied by way of Signal Input No. 3 (changing Vs). In

each case a change is made at 15:10 microseconds that changes the delay through the tube from 5 to 10 microseconds. In Fig. 5A, it can be seen that the time between successive pulses emerging from the tube is increased slightly for a period long enough to accumulate 5 microseconds. In Fig. 5B, however, an interval of 5 microseconds is suddenly inserted in the chain of pulses. This last type of change is a particularly desirable one.

Stating it somewhat differently, the impulse entering upon the helical path between the cathode and the collector can be caused to arrive at the collector end of the tube ahead of other impulses which originally preceded it. By this means a complete distribution or shuiliing (in time) of a sequence of V:impulses can be accom- `plished.

Various alternative forms of the arrangement shown in Fig. 1 are possible and some of these changes will now be described. The exterior solenoid coil I3 can be replaced by a permanent magnet such as that shown in the arrangement of Fig. 4. For simplicity of the drawing, only the annular envelope I4 has been shown but it is to be understood that the electron gun elements I6, the collector electrode I1, the means for obtaining the electric fields and the toroidal coil I2 are the same as the corresponding elements in Fig. 1. The permanent magnet structure comprises a cylindrical permanent magnet 60, magnetic end plates 6I and 62, and a multiplicity of discs 63 and annular plates 64 to reduce transverse components of the magnetic field. The arrangement of Fig. 4 produces a eld Bz as in the embodiment I0 of Fig. 1 although it is more difficult to make changes in the magnetic eld strength than in the previously described cmbodiment.

Another alternative is to replace the toroidal coil I2 in the arrangement of Fig. 1 by a solid conductor or by a series of concentric conductors carrying heavy currents.

'I'he collector ring I1 can have one or more insulated sectors to reduce the eiTects of velocity dispersion and to achieve a quantized time delay. One of the main problems connected with the delay tube is the dispersion of a transmitted pulse due to the thermal spread of velocities at the cathode. In considering means of improving this situation, it is to be noted that electrons with diierent initial velocities not only arrive at the collector at diierent times but follow diierent orbits. Thus, a group of electrons of different velocities will arrive at the collector along different paths and will strike diierent portions thereof. A group of electrons confined to aparticular velocity range can be selected by dividing the collector ring 'I0 as shown in Fig. 6 and taking'the output signal only from a small section 'I2 thereof. The pulse observed in this way will be less dispersed. Furthermore, the delay through the tube will be quantized by this arrangement. Thus, as the accelerating voltage' is changed, transmitted pulses'willrbe observed only at certain spaced intervals of delay. The intervals can be made as small as desired byspacing several active segments 'M around the collector (as shown in Fig. 7), these being connected together.

In some embodiments the shell I8, the eiect of which is to assist in establishing the proper physical path A by its repelllng effect upon the electrons therein can be omitted, and in some embodiments the solenoid winding I3 for proaccents ducin'g the l.longitudinal :magnetic v'.-eld :can falsofbezomitted.

yof fth'e "principles tof the invention. "Numerous modifications .may be .'devised byvthose skilled in the art vwithoutadeparting kfrom z.tlfiefFspi'rit Land Scopefoffth'einvention.

What isrclaim'edis: l

1. A cathode-ray device comprisinganfannular evacuated chamber, ,fanelectron gun near oner'end of 'fsaid-.chamben 1 'a rcollecting Aelectrode Ineai` the other :end of said chamber; andmeans .for'directing-electrons Tfrom fsaid Ygun ytofsaid fcoll'ectin-g electrode in :a 'hellical vpath through fsa-id bei?, fsaid :means fincluding Ia -metallic cylinder Within zsa-id chamber extending-f fromffthe vicinity of said gun to the Vicinity of said collector.

f2. :The combiii'atien fofelem'e'nts asin claim' 1 inf-umher:combinationfwith means-for applying afsignal :to Vsaid-cylinder.

yA=cathoderaydevicefcomprising an annular evacuated fcha'mber, an telectron -gun fnear Y one en'd of Saidcha-mber, fa collecting--electrodeanear the tether .end of said fcl/rambery and :magnetic means yfor 4directing felectrons from :said "fgun' to said collecti-ngfelectrodeffin-fa helioalipath through said Ichamber, said magnetic 'means including means `for @establishing a longitudinal .magnetic eldand means .for establishing a i circumf erential magnetic-incid.

A. 'A methode-.ray devi'ce ,comprising v an fannularfevacuated'chambenian electrongunnear-ene end of ysaid chamber, fan-collecting electrode near the other fen-d of Y, said chamber :and :magnetic means A.for `:directing Y ielectrons from saidffgun .to sai-dscollectingfelectrode inahel-i-cal path throughsaid` chamberfsaid -lastementioned means vincluding a solenoid around said evacuated chamber anda-a Ator oidal coil-associated therewith.

i5. -Acathode-raydevice-comprising an annular evacuated-chamber, anelectron gunnear 'one end of said chamber, -a --collecting =electrode structure near theeother end -otsaid chamber and means fordirecting .electrons fromsaid g-unto saidcol-lecting electrode structure =in ya1-helical pathv through `said-chamber, said collecting electrode .structurexhaving-a 4segment therein `which is insulated zfrom the-restof `4the` collecting electro de structure.

f6. -A `cathode-.ray 4device `comprising an. annular evacuatedchamber, anelectron gun .near one end '.of .said chamber, .aY .composite collecting electrode structure near the other-end of v.sa-id chamber, .andmeans for directing .electronsifrom saidZ gun to. saidcollectingelectrode structure v1in a' helical .paththrough.saidchamberrsaid collecting electrode structure having .a multiplicityof segments v.therein which lare rstructurally spaced and insulated Afrom each other, alternate segments -being `connectedtogether.

7. A cath'ode-raydevi'ce comprising an ann-ular evacuated chamber, an electron gunnearone .endo'f said.chamber, a collectingelectrode'.nearA the .other Vend-of Ysaid chamber, .and magnetic 6 means fior .directing electrons yfrom=.said..gun to saidcollecting. electrodein a helical pathfthroug-h said chamber, said 'magnetic mea-ns comprising arpermanentzmagnet: structuresutroundingz) said evacuatedlchamber. y

8. A cathode-ray device-f comprisngfantannular evacuated chamber,..an-.electron gun near one end of said chamber,a collecting eleotrodanear the other end of said chamber, and .niagnetc means for directing electrodesr'omsaid-gunto said collecting electrode in a helical path'through said chamber, said magneticameans.comprisinga permanent magnet structure surrounding said evacuated chamber, ia. multpiicity of annular rings within said permanent magnet structure and surrounding said evacuated-chamber, andra plurality for discsoutsidesaid'evacuated cnamberabut'fwithinthefconnnesitheref.

9. In a variable time delay electronic ffevce,

an evacuated envelopehaving an axis, means`y` within said envelope I*fr forming an electron beam, electrical means for causingthe .electrons injsa'iu "electron beam. to i'oiiowza substanuauy helicalpath about s'a`i`d axis,"means'"for.inducine a "circumferential "magnetic iield about ,said v. axis in 'the 'space 'lthr'o'ugh 'which "said lectrons travel,`means to control "the 'radia'lforce acting on said electrons, and means forco'llectingtheLee trons'rom said: electron beam.

10. An electronic device as set'\`forthl in cla'im' inwhich, rsaid"electron collecting .means is a ifsegmente'delectrodehavingfiits active portions located-symmetrically about said axis.

.71.1. Inl combination, Yan evacuated envelopeftwo substantially n'coaxial .electrodes forming a passagewayfw'ithin "said .'eva'cuatedenvelope, electrical means V'coup'ledtto"said Velectro`d'es"'for 'varying the 'radial electrical'ielfd' therebetween, rlectron gun means "adiacent'-one end '.of 'said -pas-- sageway ifor introducing "an electron'beam into said passageway,A induction rneans Yproviding a magnetic; eld "Having 'substantial' circumferen'tim cent the `other fend "of said passageway' for 'collecting the electrons from "said 'electrongun 12. Tli-eevl'ceasfset' forth Iin'z claim 11 r`lrrv'vhc'li meansare'provided for Yva'ry'mg'the outputveloc- 

